First prepare the cream: whisk egg, sugar and vanilla sugar together. Place it over steam and add white chocolate, and stir until it is molten and it thickens, about 5 minutes. Set aside and let it cool. After stir in butter and lemon juice and zest. For the cookies sift powder sugar, flour, add vanilla sugar, egg yolk, a pinch of salt and lemon zest. Knead a dough while adding butter in chunks. Roll out and cut in any shape you desire. Bake for about 10 minutes on 180°C. Let it cool and cover half of the cookies with molten chocolate and sprinkle with coconut flakes. Smear cream on the other halves and put them together.